Guided colloidal crystallization
Ng, Eric Chin Hong
Date of Issue2018-08-07
School of Materials Science and Engineering
Singapore-MIT Alliance Programme
The expanse of single crystallinity in two-dimensional colloidal crystal is limited by the difficulty to control its nucleation, leading to multi-domain growth, empty bands and voids. Using a straight nucleation line, this thesis demonstrates techniques to engineer preferential nucleation and in-plane growth of monolayer colloidal crystal in both convective-induced self-assembly and electric field assisted self-assembly. In convective driven self-assembly, a straight nucleation line is achieved by pinning the air-liquid-solid contact line along the edge of a straight surface relief. With evaporation, convective driven particle flux to the edge of surface relief enables the formation of a perfect nucleation seed, followed by subsequent in-plane growth to produce large area single domain of monolayer colloidal crystal. A model describing the criteria for successful meniscus pinning near the surface relief is proposed, with consideration of surface relief height. A similar surface relief with conductive coating is used in electric field assisted self-assembly, to attract particle accumulation and ordering by both Dielectrophoresis (DEP) and AC Electroosmosis (ACEO) forces, respectively. Near the surface relief of an electrode, preferential particle adsorption and nucleation of colloidal arrays are achieved, giving rise to in-plane growth of monolayer colloidal crystal. In addition, by analysing DEP and ACEO using finite-element method, DEP is found to be crucial in the nucleation of colloidal crystal near the surface relief, preceding the growth driven by ACEO forces. Lastly, both convective-induced selfassembly and electric field assisted self-assembly using straight surface reliefs are compared in terms of crystal quality, processing advantages and limitations. In conclusion, both approaches enable <11> (or <10>) crystal-packing directions aligned next to the straight surface relief, leading to the success of guided colloidal crystallization.